Isotropic exchange interaction between Mo and the proximal FeS center in the xanthine oxidase family member aldehyde oxidoreductase from Desulfovibrio gigas on native and polyalcohol inhibited samples: an EPR and QM/MM study

Abstract

Aldehyde oxidoreductase from Desulfovibrio gigas (DgAOR) is a homodimeric molybdenum-containing protein that catalyzes the hydroxylation of aldehydes to carboxylic acids and contains a Mo-pyranopterin active site and two FeS centers called FeS 1 and FeS 2. The electron transfer reaction inside DgAOR is proposed to be performed through a chemical pathway linking Mo and the two FeS clusters involving the pyranopterin ligand. EPR studies performed on reduced as-prepared DgAOR showed that this pathway is able to transmit very weak exchange interactions between Mo(V) and reduced FeS 1. Similar EPR studies but performed on DgAOR samples inhibited with glycerol and ethylene glycol showed that the value of the exchange coupling constant J increases ~2 times upon alcohol inhibition. Structural studies in these DgAOR samples have demonstrated that the Mo-FeS 1 bridging pathway does not show significant differences, confirming that the changes in J observed upon inhibition cannot be ascribed to structural changes associated neither with pyranopterin and FeS 1 nor with changes in the electronic structure of FeS 1, as its EPR properties remain unchanged. Theoretical calculations indicate that the changes in J detected by EPR are related to changes in the electronic structure of Mo(V) determined by the replacement of the OHx labile ligand for an alcohol molecule. Since the relationship between electron transfer rate and isotropic exchange interaction, the present results suggest that the intraenzyme electron transfer process mediated by the pyranopterin moiety is governed by a Mo ligand-based regulatory mechanism.

Magnetostructural Characterization of Oxalamide Dihalo‐Bridged Copper Dimers: Intra‐ and Interdimer Interactions Studied by Single‐Crystal Electron Spin Resonance Spectroscopy

“…Thec orresponding comparison for the [CuL V (m-Br)] 2 and [CuL A (m-Cl)] 2 complexesi so mitted because of the experimental observation of mostly collapsed lines. Whereas Equation (6) describes the data well over abroad angularrange, there is arelatively wide range of angles for which the lines are mergeda nd data cannotb ed escribed by Equation (6). As we will show in the next section, this disagreement is ac onsequence of interdimer interactions.…”

“…The characterization of exchange-coupled transition-metal complexes has become am ultidisciplinary research field with applicationsi np hysics, chemistry,a nd biology.T he information obtained from these studies is important for the design of new materials with predictable magnetic properties and moleculebased magnets [1][2][3] and to understand electron-transfer reactions in proteins. [4][5][6] The study of dinuclearc opper(II) complexes, as the simplest coupled magnetic systems with an S = 1/2 spin pair,h as an essential role in the field of molecular magnetism [7] and al ot of effort has been put into investigating the magnetic properties of theses ystems in relationt ot heir structuralf eatures. [8][9][10][11] Generally,i nd inuclear compounds, spin-spin interactions are determined by the isotropic exchange constant, J,a nd by anisotropic interactions such as symmetric anisotropic and antisymmetric Dzyaloshinskii-Moriya exchange and dipolar magnetic coupling.…”

EPR as a Tool for Study of Isolated and Coupled Paramagnetic Centers in Coordination Compounds and Macromolecules of Biological Interest

“…When this information is unknown, as is the case for Aor, the eigenvectors of the Mo V and FeS1 g ‐matrices can be proposed on the basis of the symmetry arguments described in Section 4.1. Details on how to perform this type of calculation can be found in references6e and 59. Simulation results (red spectra in Figure 14) show that the FeS1–Mo V exchange interaction J is increased roughly twofold in the EDO‐ and GOL‐treated samples relative to that determined for the dithionite‐reduced as‐prepared sample, which would suggest that the electron‐transfer pathway is modified upon inhibition.…”

“…The three simulations were performed with use of the same D ‐matrix ( D x = y = 3.98 × 10 –4 cm –1 and D z = –7.96 × 10 –4 cm –1 ) and J = –16.6 × 10 –4 cm –1 in spectrum (a) and J = –33.3 × 10 –4 cm –1 in spectra (b) and (c). The remaining EPR parameters and simulation details can be found in reference 6e…”

Transition from isolated to interacting copper(ii) pairs in extended lattices evaluated by single crystal EPR spectroscopy

“…[1][2][3][4] The information gained with these studies has been essential to establish the underlying molecular bases to design not only paramagnetic materials with predictable magnetic properties 5,6 but also to design materials such as molecular-based and single-molecule magnets. [12][13][14][15][16] Thus, the characterization of exchange coupled systems is nowadays a multidisciplinary research field since its applications in chemistry, biology, and physics. [12][13][14][15][16] Thus, the characterization of exchange coupled systems is nowadays a multidisciplinary research field since its applications in chemistry, biology, and physics.…”